Vapor compression type air conditioning systems are well known and widely used for controlling temperature in residential and commercial applications. In addition to the sensible temperature within the space controlled by a vapor compression type air conditioning system, it is usually desirable to also control the absolute and relative humidity to enhance the comfort of occupants of the space or to meet other requirements of temperature and humidity within the space.
A type of vapor compression air conditioning system has been developed wherein an additional heat exchanger is placed in the supply air flowpath which furnishes conditioned air to the space being controlled so that, in addition to cooling the supply air to reduce the absolute humidity, the supply air is then reheated to a desired temperature for comfort; and wherein the relative humidity is then also reduced for comfort and for meeting certain other requirements of the controlled space. However, some heat pump systems with enhanced dehumidification have a refrigerant fluid bypass from the liquid line to the suction line. This is necessitated by the need to return refrigerant from inactive components to the active flow path, and because of the slow transition time of a heat exchanger control valve actuator, may result in compressor flooding.
With regard to heat pump systems, it is also known that pressure and temperature conditions could be established in the system during the heating mode that make it possible for refrigerant to migrate to the charge reservoir and to the reheat coil. This condition results in the system behaving as though it is undercharged during the heating mode.
An explanation of the operation of a heat pump system in these modes will better explain the problems encountered. Referring initially to FIG. 1, illustrated is a conventional vapor-compression type air conditioning system 100 with enhanced dehumidification accessory as disclosed in U.S. Pat. No. 6,826,921. The vapor-compression type air conditioning system 100 is also operable in a reverse or so-called heat pump mode. Dashed line 60 divides the outdoor components of the system (left side of FIG. 1) from the indoor components (right side of FIG. 1) for conditioning air within a space 32. The outdoor part of the system 100 includes a motor driven compressor 132 operably connected to a remotely controllable system reversing valve 136. A condenser heat exchanger 138 is operably connected to system reversing valve 136 via a conduit 140 for receiving high pressure refrigerant fluid from compressor 132 by way of reversing valve 136 when valve 136 is in position X, as shown. Condensed high pressure fluid flows via a conduit 142 to a conduit 144 leading to a first motor operated valve 146.
A conventional arrangement for heat pumps of an expansion device 150 in series with a filter/dryer 147 is employed. A check valve 148 is in parallel with expansion device 150 and filter/dryer 147. The check valve 148, expansion device 150 and filter/dryer 147 are interposed heat exchanger 138 and conduit 142. In like manner a conventional arrangement of an expansion device 154, a filter/dryer 157 and a check valve 156 are operable to be connected to conduit 144 via valve 146. An indoor heat exchanger or evaporator 158 receives refrigerant fluid from the conduit 144 and valve 146 through expansion device 154 whereby cooling effect of air being pumped by a blower 160 to the conditioned space 32 is provided as heat exchange takes place through the heat exchanger 158. Heat exchanger 158, as well as a reheat heat exchanger 162, may be disposed in suitable ductwork 174 for conducting return air from blower 160 to supply conditioned space 32. For normal operations, return air to the heat exchanger or evaporator 158 is drawn from conditioned space 32 through a return duct 173 by blower 160. Refrigerant fluid exiting the evaporator heat exchanger 158 flows through a conduit 164 to the reversing valve 136. The air conditioning system 100 further comprises a refrigerant fluid charge compensator 180 interposed conduit 164 and conduit 166, and is further coupled to a branch conduit 182. Conduit 182 is connected to the refrigerant fluid path comprising that portion of conduit 175 between the heat exchanger 162 and a second motor-controlled valve 170. Charge compensator 180 comprises a closed heat exchanger vessel which is configured to store refrigerant fluid, generally in liquid form, under certain operating conditions wherein an excess refrigerant fluid charge in the system 100 would otherwise adversely affect the operation thereof. In the normal cooling mode as illustrated in FIG. 1, refrigerant flows through conduit 164 and the charge compensator 180 to the reversing valve 136. The position X of the reversing valve 136 in the normal cooling mode of the space 32 causes refrigerant fluid in vapor form to flow through conduit 166 from valve 136 to the compressor 132. As mentioned previously, compressed refrigerant fluid discharged from the compressor 132 flows through valve 136 to conduit 140 to complete a circuit.
The second motor-controlled valve 170 is operably connected to: conduit 164 after the charge compensator 180, conduit 175, and the reheat heat exchanger 162, as shown. Furthermore, the system 100 may include a bypass conduit 172 and pressure relief valve 174 for bypassing fluid around heat exchanger 138 from conduit 140 to conduit 142. Heat exchange takes place at the heat exchanger or condenser 138 by flow of ambient outdoor air through the heat exchanger 138 as propelled by a variable speed motor-driven fan including fan blade or propeller 184 drivingly connected to a variable speed motor 183. A controller 186 receives signals from humidity sensor 30 and temperature sensor 34 within conditioned space 32 for controlling compressor 132, fan motor 183, and a motor 161 for driving blower 160. Controller 186 also controls the positions of the valves 146 and 170. Valve 146 is operable to conduct refrigerant fluid from conduits 142, 144, in turn to expansion device 154 and heat exchanger 158. Valve 146 is also operable to conduct fluid from conduits 142, 144, in turn, via a conduit 143 directly to reheat heat exchanger 162 which is located downstream with respect to the direction of airflow or supply air from blower 160 to space 32, as indicated by the arrow 171 in FIG. 1. Valve 170 is operable to communicate fluid from heat exchanger 162 to conduit 164 or to conduit 175 which, as shown, is connected to conduit 144 between valve 146 and expansion device 154. The operation of valves 146 and 170 will be discussed below.
In operation of the system 100 for providing cooled, conditioned air to the space 32, the controller 186 will call for operation of the compressor 132, the blower motor 161, and the fan motor 183 to operate the system 100 in the normal cooling mode, that is with high pressure refrigerant vapor being discharged from compressor 132 to flow through condenser heat exchanger 138 and check valve 148; then through conduits 142, 144, valve 146 and dryer 157; then through expansion device 154, and through heat exchanger 158 to absorb heat from air being blown through the heat exchanger by blower 160. Valve 146 is in the position shown in FIG. 1 and valve 170 is in the position shown, which essentially isolates heat exchanger 162 since no refrigerant fluid flow occurs therethrough. Low pressure refrigerant fluid in vapor form is returned to compressor 132 via conduit 164, reversing valve 136 and conduit 166.
With the system 100 in the cooling mode, as shown in FIG. 1, valve 146 directs all refrigerant fluid flow to the expansion device 154 and the heat exchanger 158 and with the valve 136 in position X to allow flow of fluid through conduit 164 to the inlet or suction side of compressor 132, the compressor will also withdraw liquid refrigerant from the heat exchanger 162 while it is inactive, thanks to the position of valve 170 shown.
Referring now to FIG. 2, illustrated is the conventional heat pump system of FIG. 1 in cooling mode with enhanced dehumidification engaged as disclosed in U.S. Pat. No. 6,826,921. Compressor 132 still delivers high pressure refrigerant fluid vapor to condenser heat exchanger 138 since valve 136 remains in position X. Partially condensed refrigerant fluid flows from heat exchanger 138 through conduits 142, 144 and valve 146, now in a position to conduct refrigerant fluid, partially or completely condensed, through heat exchanger 162 to exchange heat with air flowing to the space 32 via the blower 160 and the heat exchanger 158. Further cooled refrigerant fluid flows through valve 170, in its position as shown, and through conduit 175, dryer 157 and expansion device 154 before absorbing heat from air flowing through heat exchanger or evaporator 158. As controller 186 receives signals from the humidity sensor 30 requiring even lower relative humidity the fan motor 183 is operable to reduce the speed of fan 184 to reduce the heat exchange taking place at condenser heat exchanger 138 and places a greater condensing burden on the heat exchanger 162.
When the valves 146 and 170 are positioned as shown in FIG. 2, partially condensed refrigerant fluid from the heat exchanger 138 flows through heat exchanger 162 before going through the expansion device 154 and evaporator or heat exchanger 158. The controller 186 is operable to reduce the speed of fan motor 183, as required by the sensor 30, to a point where there is no longer complete condensation of refrigerant fluid in the heat exchanger 138. Pressure relief valve 174 will allow bypass of compressor discharge gas around the heat exchanger 138 when a pressure differential across the heat exchanger 138 exceeds a predetermined level. Accordingly, energy efficient tempering of air being supplied to the space 32 is provided. In certain instances the pressure relief valve 174 may or may not be required.
It should be apparent to one who is of skill in the art that the repositioning of reversing valve 136 and valves 146, 170, in addition to reconfiguring the system for a different mode, also causes fluctuations/surges as some residual pressure differentials undoubtedly exist in the system.
Accordingly, what is needed in the art is a device that prevents unwanted refrigerant flow during heat exchanger control valve transition or the heating mode.